Field of the Invention
The invention pertains to the field of cutting tools. More particularly, the invention pertains to a multi-flute cutting tool having a flute that is W-shaped in cross section for superior chip evacuation (i.e., removal of swarf).
Description of Related Art
A conventional milling cutter 100 is illustrated in FIGS. 8-10. The cutter 100 has a cutting head 102 and a coaxial integral shank 103 for securing in a chuck or arbour of a machine tool for rotation about an axis X.
The cutting head 102 has a plurality of helical flutes 105 extending from a leading end 106 of the head 102, to a trailing end 107 of the head 102. Each flute 105 has a tooth 108 provided with a leading face 109 and a rear face 110, as shown in FIG. 10. The leading face 109 faces the direction of rotation of the cutter 100 when in use and has a cutting tip 104.
As shown in FIG. 10, each tooth 108 also has a primary relief rake facet 111 which, in the example illustrated, is planar. The primary facet 111 comprises a land, which extends rearwardly from the tip 104 of the leading edge 109 of the tooth 108 to a heel 115.
The leading face 109 of a trailing tooth 108, and a rear face 110 of the immediately preceding tooth 108 diverge and define, together with a flute base 113, a gully 114. The gully 114 is provided for swarf removal purposes and is designed so that in use the swarf generated during cutting is carried away without clogging the cutter. This is achieved by controlling the pitch of the teeth, the depth of the gully 114 and the width of the land of the primary facet 111.
As described above, the geometry of rotating cutters includes many features and elements, each of them playing a role in achieving desired performance goals. The most basic geometry element is a flute, otherwise known as a groove, a plurality of which forming rake edges, rake faces, teeth and eventually serving as a chip (i.e., swarf) formation and evacuation channel. The flute geometry or flute shape makes the difference between success and failure in workpiece milling applications. Conventionally, the rake face, flute core and flute back is formed by a single movement (i.e. grinding path), where cross sectional shape of the flutes are formed as a result of mathematical calculations based on input including the flute core, rake angle, depth of the rake angle measurements, tooth width (or attack angle), grinding wheel shape and flute core profile along the axis of rotation.
The aforementioned input imposes strict bounds for the calculations, resulting in certain flute shapes to be mathematically impossible to achieve. As a result, the majority of flute cross-sectional shapes have very much in common that relies on having as much as flute depth as possible, while maintaining the desired tooth width to provide the desired volume for chip evacuation.
The disadvantage of the common flute shape can be seen in the resultant shape of the rear face 110 of the flute 105, where a bulge of substrate material is left, thereby reducing the volume of the flute 105 without adding much strength. This disadvantage becomes much more distinct when implementing multi-flute milling cutters with seven (7) or more flutes. Shortage of available space impose an insolvable task for common flutes to provide enough volume for chip evacuation, while providing sufficient tooth width. As a result, many conventional multi-flute cutters have problems with the adequate evacuation of chips.